1. Field of Invention
This invention relates to a somatic element of single crystalline sapphire (.alpha.-Al.sub.2 O.sub.3 :corundum) ceramics used as an implant for dental surgery or an implant for orthopedic surgery and to a method of manufacturing the same.
2. Prior art
Heretofore, metal (for example, stainless steel, Co--Cr alloy, metallic titanium, metallic tantalum, Ni--Cr alloy, etc.) has been used as a material in a somatic element of the kind described. However, the somatic element of such metal is in most cases inferior in so-called "affinity" with (adhesibility to, wettability with) its ambient tissue and in addition, there is a possibility of the somatic element tending to be ionized by saliva, secretion of the mouth, food, body fluids, blood and the like thereby producing harmful effects as a result of metallic ions in the human body. To cite a positive instance of such a fact, it is reported that in the case of stainless steel most generally used as a somatic element for orthopedic surgery, it is necessary to perform a repeated operation on the affected region to extract the element therefrom in a certain period of time after the operation. On the other hand, in the case of a somatic element of polycrystalline ceramics, the element is excellent in affinity with its ambient tissue and chemically highly stable, thereby having no necessity of extracting the element from the implanted region after the operation, but has the disadvantage of it being inferior in mechanical strength to a metallic member. In view of this fact, the present applicant has provided various inventions for improvements in the mechanical strength of a somatic element of ceramics. The somatic element proposed heretofore by the inventions is dependent upon the structure of the element itself for the postoperational strength of the implanted element. For example, in the previous U.S. patent application, Ser. No. 550,186, 1974, such structural consideration was given to the tightening force produced by threadedly fitting a nut over the top of a screw type implant pin of ceramics embedded in the bone tissue (and if necessary, over the bottom part of the pin that projects through the bone tissue) and used to fix the implant pin to the bone tissue so that the implant pin could cope with outer force such as repeated occlusal impact imparted to the pin after the implantation. Similarly, in the previous U.S. patent application, Ser. No. 674,688, 1975, by the present applicant, structural consideration was given to the manner that a screw type implant pin of ceramics was provided in the circumference with a horizontal flange, the horizontal flange acting as a stabilizing seat since the flange is fitted closely into the counterbore formed in a cortical bone (hard tissue) when the pin is threadedly inserted into the bone so that the pin could withstand the outer force to be later applied thereto.